Casting JSONValues arrays to native arrays ... ??? ...

[james.p.leblanc]

Dear D-ers,

In attempting to cast JSONValues that hold arrays to "native" 
array types,
I have hit some issues.  Example code:

```d
import std.stdio;
import std.json;

void main(){

    JSONValue jj;
    jj["d"] = [ 1.234 ];                  // a "dummy" double value
    jj["ba"] = [ true, false, true];      // "ba" boolean array

    writeln("typeid(jj): ", typeid(jj), ", jj: ", jj );

    // various things that I thought might work, but do NOT

    auto z1 = cast(bool)   jj["ba"];           // attempt #1
    auto z2 = cast(bool[]) jj["ba"];           // attempt #2
    auto z3 = cast(bool)   jj["ba"].array;     // attempt #3
    auto z4 = cast(bool[]) jj["ba"].array;     // attempt #4
    writeln("typeid(z4): ", typeid(z4), ", z4: ", z4 );

}
```
Attempts 1,2, and 3 yield compilation errors (which I somewhat 
understand):

question.d(12): Error: cannot cast expression `jj.opIndex("ba")` 
of type `JSONValue` to `bool`
question.d(13): Error: cannot cast expression `jj.opIndex("ba")` 
of type `JSONValue` to `bool[]`
question.d(14): Error: cannot cast expression 
`jj.opIndex("ba").array()` of type `JSONValue[]` to `bool`

However, if I comment out the offending attempts (1, 2, and 3), 
then it
compiles, and can run ... but produces a result which I very much 
do NOT
understand:

typeid(jj): std.json.JSONValue, jj: 
{"ba":[true,false,true],"d":[1.23399999999999999]}
typeid(z4): bool[], z4: [false, false, false, false, false, 
false, false, false, false, false, false, false, false, false, 
false, false, true, false, false, false, false, false, false, 
false, false, false, false, false, false, false, false, false, 
false, false, false, false, false, false, false, false, true, 
false, false, false, false, false, false, false, false, false, 
false, false, false, false, false, false, false, false, false, 
false, false, false, false, false, true, false, false, false, 
false, false, false, false]

Hmmmm... is there a standard way to push these JSONValues into 
nice native
array types? (The real code is eventually going to be using 
traits and mixins
... but I do not think this should pose additional problems).

All help and illumination thankfully received.
Best Regards,
James